Electrical Instructions for Replacing the Generator with a GM Alternator in a Spitfire MKI, MKII, MKIII, or a GT6 MKI
by Dan Masters, danmas@aol.com
Important Note: this entire article assumes a previous conversion to negative ground!
Method One (Utilizing existing wiring)
- At the control box, look for the following wires:
Black
Remove and discard.
Small Brown/Yellow Brown/Green
Disconnect and tie together, with an insulated connector.
Large Brown/Yellow
Brown (3)Using a large, solder type butt connector, connect all 4 of these wires together, and insulate with heat shrink tubing. Be aware - this connection carries ALL of the current for the car, so it must be a good connection. You do not want a high resistance here. You may have to go to an electrical supply house for this type connector, rather than an auto supply store, to get one large enough to hold all 4 wires. Run two wires into one end of the connector, and the other two into the other end.
Remove the control box and, please, save for a friend who is a purist!
- At the old generator, you will find two wires, Brown/Green and Brown/Yellow. Disconnect them from the generator and leave in place. Remove and save the generator.
- At the new alternator, on the side of the case, you will find two spade lugs recessed into the body. The lugs are identified on the body of the alternator as 1 & 2. You will need a plug (connector) for these. These plugs are readily available at an auto supply store, usually in a package hanging on the pegboard display rack in the electrical section, and usually identified as an alternator extension connector, or something similar. If not, the counter man will know what you are looking for. There will be two short wires already connected to the plug.
On the back of the case, you will find an insulated screw terminal.
Connect the Brown/Green wire to the plug wire going to the # 1 terminal, using a butt connector, or splice, solder, and insulate with heat shrink tubing. The plug is keyed, and will only go in one way. Connect the other lead from the plug (#2) to the screw terminal on the back of the alternator case, along with the large Brown/Yellow lead from the original harness, using ring terminals. Both the large Brown/Yellow wire and the wire from terminal #2 connect to the screw terminal.
Disconnect the ground lead from the battery before proceeding with any electrical work, and, of course, follow all the rules of proper wiring practices. I recomend using solder connections, and covering them with heat shrink tubing, but crimp type connectors will work quite well also. You will need butt connectors for attaching to the plug wires, and a large ring connector for the screw terminal. If you would prefer not to have splices, you can remove the terminals, and the wire, from the plug. Using new terminals of the proper type, connect directly to the existing wires, and insert the terminals into the plug. New terminals can be purchased from British Wiring, (20449 Ithaca, Olympia Fields, IL 60461, 708-481-9050) and The Wire Works (167 Keystone Road, Chester, PA 19013, 800-292-1940), among others.
You are finished!
There are two things, however, to be aware of:
- Triumph did funny things when they built these cars, so your car might not match the configuration above, and it may well have been modified by a previous owner.
- You now have an alternator capable of more than twice the output of your old generator, but the wiring capacity has not changed. If you add heavy loads, driving lights, high power stereo, etc, you can exceed the capacity of the wires. Also, If you let the battery discharge completely, the alternator can possibly recharge with enough current to overload the wires. If your battery is completely discharged, recharge it with a charger rather than push starting the car and letting the alternator recharge it. Under all other usages, the wiring should not present a problem. The main advantage of the higher output is the ability to provide a higher charge rate at low RPM and idle. The standard loads on Spitfire or a GT6 do not require a higher charge current at normal engine speeds, so the alternator will not be called on to provide enough current to overload the wires.
Method Two (Upgraded wiring)
If you wish to upgrade the wiring to take advantage of the higher output, it is really quite simple.
As above, except:
Cut off both ends of the large Brown/Yellow wire - at the old generator and at the control box - as close to the wire harness wrapping as possible (or, unwrap the harness, and remove the wire all-together).Connect the three Brown wires together at the control box.
Instead of connecting the large Brown/Yellow wire to the new alternator, add a new wire of at least 10 Ga (8 Ga preferred). Connect one end to the screw terminal at the alternator, and the other end to the terminal on the starter solenoid where the main cable from the battery and a 2 Brown wires are now connected. Leave the existing wires at the solenoid connected. Very carefully route this new wire alongside the existing wiring harness, and use cable ties liberally for support.
Now, the alternator can provide full charging current without worrying about burning up the wiring.
If you wish to add extra loads, such as a high power sound system, connect them directly to the battery, properly fused, of course. Loads connected directly to the battery will not be indicated on the ammeter.
Options
You may wish to add a voltmeter. If so, simply connect the plus terminal of the voltmeter to any convenient Green wire, and the minus terminal to a good ground point. One side of the ilumination lamp inside the voltmeter should be connected to the most convenienet Red/White wire, and the other side should connect to a good ground point (unless the lamp is grounded to the meter case. If it is, ensure that the case is properly gronded to the metal dash structure).
You may also choose to use a different alternator , rather than the GM unit. If so, it will be wired very similarly to the above, only the connections at the alternator itself will be different.
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